A Little Bit More
Although adult dragonflies and damselflies are a common sight in warm weather, their immature aquatic counterparts are not nearly as well known. Just like the adults, nymphs have voracious appetites, and prey upon a wide range of small, and sometimes not-so-small, organisms. Fish hatcheries occasionally have problems with nymphs eating large numbers of their baby fish, but for the most part, their diet consists of other invertebrates.
Dragonfly nymph © Solon Morse
Probably the most interesting single feature of dragon and damselfly nymphs is their extendible labium or lower lip as shown in the unit poster. Nymphs usually lie quietly in the vegetation or under bottom sediment waiting for unsuspecting prey. When prey comes within range, the labium can be shot forward to catch the animal with two movable, claw-like lobes at the tip. This entire structure, when fully extended, is usually one third the entire length of the nymphs’ own body!
Dragon and damselfly nymphs are relatively easy to distinguish one from the other: Damselfly nymphs have three large leaf-like gills at the end of their abdomen or smaller gill tufts along the sides of their abdomen, while dragonflies have internal gill structures that are not visible on the outside.
Activities
Science – Pet Dragon
Objectives: See how the dragonfly nymphs feed
Materials: cake pan, plastic wrap, dragonfly nymph, mosquito wigglers
This is an activity that will require a bit of preparation (you’ll need to collect some animals) but is one that will instill in all observers, the fact that life in a pond is not so serene! You’ll be able to see, first hand, how the dragonfly nymphs capture their prey.
- Go to almost any local pond or still body of water where there are lots of water plants, especially floating plants like anachris (elodea) or cabomba (fanwort). Gently pull handfuls of plants out of the water and check carefully for dragonfly nymphs clinging to the plants. They should be rather easy to spot as they cling to the plants. There will be a range of sizes but you’ll probably find the larger ones best for this activity.
- Bring one or two nymphs home in water along with a few plants and place in a shallow cake pan with a couple inches of water from the pond. If you can find mosquito wigglers around your area (these will be in stagnant water) you’ll have a good source of food for your nymphs. Place these in a different small container of water as your food source.
- Allow a day or so for the nymphs to settle in. Keep a plastic wrap or screen over the container to prevent their crawling out.
- When you’re ready, take a few wigglers from your “food source” and slowly pour them into the pan with the nymphs. Observe without disturbing the nymphs and watch for the wigglers and nymphs to close the gap (you may need to use a thin instrument to gently move the wigglers close to a nymph). As the wigglers get within range of the nymphs, a hungry nymph should respond by feeding. You should be able to see their extendible mouthpart (labium) quickly reach out and grab a wiggler.
I realize that this is an activity where one animal kills and eats another and it may be upsetting for some individuals. Granted, these are mosquito wigglers that many may have no interest in seeing survive, but there are some who may. It’s always a good idea to show a respectful approach to this activity – animals need to feed but we don’t need to be sadistic about it!
Some questions you may want to discuss with your students:
- Did you notice any “preparation” on the part of the nymphs before they grabbed their prey?
- Did the nymphs ignore any potential prey? Could it have been that the prey was too large or too small or that it didn’t move?
- Did the nymphs lie on the bottom of the container or did they cling to the plants?
- Do you think these nymphs would make a good meal for predators like fish?
- At what point in the lives of the nymphs might they be most vulnerable – when they were small or when they were full-sized?
- Can you think of any ways in which a nymph might make itself less conspicuous?
- Did the nymphs see you as you approached their container?
- Did the nymphs feel you (feel any vibrations) as you approached their container? If so, how did they react?
Key Concepts
Structures and Functions, Predator/Prey Relationships, Life Cycles, Food Webs /Food Pyramids, Behavior and Regulation
Questions
Do you have a question for a naturalist? Go ahead and ask!
It's easy -- just fill out this form, submit your question and you'll receive an answer shortly.